1. Technical Field
Example embodiments of the present invention relate to a national research and development project having subject No. ITAC1090103100090001000100100, project name “University IT Research Center Promotion and Support Project,” and subject title “Research on Embedded Software Technology for Convergence Terminal.”
Example embodiments of the present invention relate in general to radio communication, and more specifically, to a cognitive radio (CR) cooperative spectrum sensing method and a fusion center (FC) performing CR cooperative spectrum sensing.
2. Related Art
Currently, radio communication technology is being researched and developed for a ubiquitous network in which any information can be exchanged with anybody, anytime, anywhere. Conventionally used for mobile communication and broadcasting, radio waves are increasingly used in other areas of life, such as traffic, medical treatment, science, and public order, rapidly driving up demand for frequency resources. This increasing demand for frequency resources is further accelerated by advances in radio communication technology. To solve the frequency shortage problem and maximize efficiency in frequency usage, CR technology for detecting vacant frequencies that are not actually being used and performing communication is attracting attention.
CR technology automatically enables desired communication by automatically detecting unused frequencies according to place and time while protecting authorized adjacent radio stations. The CR technology detects a spectrum that is dispersed at various intervals and has continuously varying occupation time, and enables the spectrum to be reused by determining a frequency bandwidth, output, modulation scheme, etc. appropriate for the environment, thereby improving the efficiency with which limited frequency resources are utilized. Since 2004, the Institute of Electrical and Electronics Engineers (IEEE) has been pushing ahead with the standardization of CR technology for a television frequency band.
CR technology is based on spectrum sensing techniques which allow a secondary user (SU) to sense the surrounding radio environment and detect a vacant frequency band that a primary user (PU) is not using. The spectrum sensing techniques include matched filter, signal feature detection, energy detection, and so on. Among the spectrum sensing techniques, energy detection can be implemented even when a feature of a signal to be transmitted is unknown, and is most appropriate in consideration of complexity and sensing time. However, when one SU separately performs spectrum sensing, the SU may not accurately detect a vacant frequency band because of hidden nodes, shadow fading, multipath fading, etc. To solve these problems, a cooperative spectrum sensing technique has appeared, in which results separately sensed by SUs are shared in an FC to determine whether or not a spectrum is occupied.
Cooperative spectrum sensing includes soft decision in which results observed by several SUs are first transmitted to an FC which then makes a final decision on the basis of the results, and hard decision in which respective SUs first determine whether or not a spectrum is used and then transmit the results to an FC which makes a final decision. When respective soft decision results of CR SUs are transmitted to an FC, frequency efficiency is degraded. Thus, hard decision cooperative spectrum sensing is frequently used.
In such hard decision cooperative spectrum sensing, whether the corresponding frequency band is vacant or in use is determined with reference to a threshold λ of energy detection. In other words, 1, indicating that the frequency band is in use, is transmitted when energy is greater than λ, and 0, indicating that the frequency band is not in use, is transmitted when energy is smaller than λ. Then, an FC makes a final decision using the CR information (0 or 1) transmitted by an SU, according to a fusion rule used in the FC.